Phytochrome controls many aspects of development in higher plants. The effects of its action, triggered by red and reversed by far red light, can be both short term and long term. Long term effects include changes in the level of a number of different enzymes. I propose to test whether phytochrome action in Lemna gibba involves control of changes in the messenger RNA (mRNA) content of the plant. I will compare the mRNA from plants receiving different light treatments by two methods: 1) comparing the translation products of the isolated mRNA by gel electrophoresis and 2) DNA-RNA hybridization of purified mRNA and complementary DNA. I will also look for a correlation between changes seen in the mRNA population and in vivo protein synthesis. I will use immunological methods to identify the mRNA for a particular protein, ribulose 1,5-disphosphate carboxylase. If this enzyme is under phytochrome control in Lemma gibba, as it is in other plants, I will see whether or not changes in the level of its mRNA are involved in its regulation by phytochrome.